Amyloidosis refers to a pathological condition characterized by the presence of amyloid. Amyloid is a generic term referring to a group of diverse but specific extracellular protein deposits which are seen in a number of different diseases. Though diverse in their occurrence, all amyloid deposits have common morphologic properties, stain with specific dyes (e.g., Congo red), and have a characteristic red-green birefringent appearance in polarized light after staining. They also share common ultrastructural features and common x-ray diffraction and infrared spectra.
Amyloid can be classified according to the protein type, as described in a recent report (Kazatchkine et al., (1993) Bull. WHO 71:105). Different amyloidoses are also characterized by the type of protein present in the deposit. For example, neurodegenerative diseases such as scrapie, bovine spongiform encephalitis, Creutzfeldt-Jakob disease and the like are characterized by the appearance and accumulation of a protease-resistant form of a prion protein (referred to as AScr or PrP-27) in the central nervous system. Similarly, Alzheimer's disease, another neurodegenerative disorder, is characterized by congophilic angiopathy, neuritic plaques and neurofibrillary tangles, all of which have the characteristics of amyloids. In this case, the plaques and blood vessel amyloid is formed by the beta protein. In other systemic diseases such as adult-onset diabetes, the protein is amylin, in complications of long-term hemodialysis , the protein is beta-2-microglobulin, in sequelae of long-standing inflammation, the protein is serum amyloid A (SAA), and in plasma cell dyscrasias, amyloids are characterized by the accumulation of light chains systemically. In each of these cases, a different amyloidogenic protein is involved in amyloid deposition.
Once these amyloids have formed there is no generally accepted therapy or treatment to dissolve the deposits in situ. There is, therefore, an urgent need for therapeutic agents which can either inhibit the formation or growth of amyloid or dissolve amyloid deposits once formed. Co-pending U.S. patent application Ser. No. 08/403,230 describes methods and compositions of sulfated and sulfonated compounds, or functional equivalents thereof, useful in the treatment of amyloidosis in vivo.
One difficulty encountered in identification of therapeutic agents for the treatment of amyloidosis is the lack of rapid, general screening assays for such agents. U.S. Pat. No. 5,164,295 describes a screening assay which measures the ability of a compound to inhibit the interaction between an amyloid protein and an extracellular matrix protein. U.S. Pat. No. 5,348,963 describes an assay which screens compounds based on their ability to alter the intracellular processing of amyloid precursor proteins in mammalian cells in cell culture. Co-pending U.S. patent application Ser. No. 08/403,230 describes a mouse model of amyloidosis which is used for screening for compounds which have the ability to decrease amyloid formation in vivo.
Another difficulty encountered in searching for treatments for amyloidosis is that the mechanism of amyloid fibril formation, although extensively studied in vivo (see, e.g., R. Kisilevsky and I. Young (1994) in G. Husby, ed. "Clinical Rheumatology: Vol. 8, No. 3, Reactive Amyloidosis and the Acute Phase Response" London: Bailliere Tindall, pp. 613-626; E. Gruys and F. W. J. J. Snel (1994) in Husby, ed., op. cit., pp.599-611) and in vitro (see, e.g., G. G. Glenner et al., (1971) Science 174:712; E. M. Castano et al. (1986) Biochem. Biophys. Res. Commun. 141:782; D. A. Kirschner et al. (1987) Proc Natl. Acad. Sci. USA 84:6953), has not been completely elucidated. In general, in vitro conditions used to cause amyloid fibril formation have not been similar to physiological conditions. The in vitro methods known in the art usually require high amyloid protein concentrations, unnatural pH ranges, or strong solvents to cause amyloid fibril formation ( see, e.g., I. B. Kingston et al., (1995) Nature Med., 1:138-142; Glenner et al, (1971) op. cit.). Thus, the amyloid fibrils formed by these methods may not reflect the structure of fibrils formed in vivo, and the conclusions drawn from structural studies of such in vitro-formed fibrils may not be applicable to fibrils formed by amyloidogenic conditions in vivo.